The present invention relates to a device for the detection of the clogging of an air filter.
The air treatment equipments and more particularly the heating and air conditioning devices of automotive vehicles are often fitted with filters adapted to retain the particles in suspension in the processed air. These filters are creating pressure losses when the air is flowing through, the magnitude of these losses being a function of the speed of the air which is flowing therethrough. During their use these filters would be loaded with dust and particles which should be retained by the filters which become gradually clogged.
This clogging of the filters induces an increase in their head loss which is harmful to the good operation of the equipments.
There are known equipments adapted to advise the user of the state of clogging of such filters. These equipments are very often based upon the measurement of the head loss exerted by the filter upon the air flow. This head loss is often compared to a predetermined value in a comparator circuit which when the head loss exceeds the predetermined value would release an alarm inviting the user to carry out a cleaning of the filtering surfaces or to provide for the replacement or causes a suitable device to become operative for overhauling the filtering surfaces, which device is often referred to as an "unclogging" device.
Such devices are effective on equipments adapted to operate with a constant air flow rate. They may however not be properly used on equipments fitted with flow rate adjusting means such as fan rotational speed variators or air flow rate shut-off flaps like those which are fitting the air conditioning equipments for automotive vehicles.
The head loss of air filters is indeed a function of two parameters at the same time:the velocity of the air which is flowing therethrough and their state of clogging.
The measurement alone of the head loss induced by the filter does not allow to distinguish the part due to each one of the two causes and more particularly it does not allow to make out at a small air flow rate whether an excessive clogging of the filter has not been reached although the ascertained head loss remains lower than a fixed limit.
In this case the prior equipments provided for the detection of the clogging of filters adapted to operate with a variable air flow rate by the processing of two data, the one originating from the measurement of the speed of the air flowing through the filter and the other one from the measurement of the head loss produced by the latter.
The method exhibits the serious inconvenience of requiring the processing of measurements performed in absolute values thereby involving precision measurements.
Such measurements require appliances which are tricky to be put in operation, expensive and not very well adapted to the requirements of the automotive vehicle market.